An ethanol reformer can be used to convert ethanol into a reformate gas (e.g., a gaseous fuel) that has favorable properties for combustion in an internal combustion engine. For example, nitrogen oxide (e.g., NOx) emissions may be reduced and engine efficiency may be improved with the use of reformate fuel. The reformer may not be able to constantly supply a desired amount of reformate to the engine, however; therefore, a storage tank may be utilized to store the reformate after it is generated and before it is injected to the engine.
In order to store a large amount of the reformate while minimizing the size and weight of the storage tank, the reformate can be stored at high pressure. The operating pressure of the reformer may be low in comparison to the high pressure of the storage tank, however, and transfer of the reformate to the storage tank may be difficult under some circumstances. As such, a pump may be used to facilitate transfer of the reformate from the reformer to the storage tank. Use of the pump, however, can impose a parasitic loss on the system which can cause degradation in fuel efficiency, for example.
The inventors herein have recognized the above issues and have devised an approach to at least partially address them. Thus, a method for a fuel system including a reformer and a storage tank coupled to an engine in a vehicle is disclosed. The method comprises, generating a gaseous fuel in the reformer; under a first condition, opening a valve to transfer the gaseous fuel from the reformer to the storage tank; and, under a second condition, operating a pump to transfer the gaseous fuel from the reformer to the storage tank.
In one example, the valve is opened when a pressure in the reformer is greater than a pressure in the storage tank. Further, an engine operating condition, such as spark timing, may be adjusted while the valve is open to further increase the pressure in the reformer and facilitate the transfer of reformate (e.g., gaseous fuel) from the reformer to the storage tank. When the pressure in the storage tank is greater than the pressure in the reformer, however, the pump may be utilized to transfer reformate to the storage tank.
By opening a valve to transfer reformate to the storage tank when pressure in the storage tank is low, operation of the pump may be reduced thereby reducing parasitic losses on the system, while still achieving transfer and storage of increased reformate in the storage tank. As such, a smaller tank may be used to store a larger amount of the reformate at high pressure without significantly reducing system efficiency.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.